Depends on how long you run them. I run two blue bulbs in the am and pm for a few extra hours each day, so I replace the blue bulbs every ten months. I have noticed a pronounced detioration near the end of the bulb life, and don't like replacing them all at once, so I start replacing bulbs at ten months (blue morning and evening bulbs) and then one a week until they are all replaced by the eleventh month. I tried going for a whole year on bulbs and the last month didn't do my corals any favors.
I agree that ATI are the best bang for your buck in the bulb department.
I don't believe you can run HO bulbs in a RO fixture.
I have used an equal number of ATI Blue special and Blue Plus bulbs and been satisfied with growth and appearance. I believed that a "whiter" bulb was necessary for good coral growth. Based on what I have read, I am no longer convinced of that. I believe the PAR values to be the primary consideration, and the appearance of the tank is a matter of personal preference. I am starting an experiment with three Blue Plus and one Blue Special bulb over my frag tank. If I don't like the results I will swap out one of the bulbs for another Blue special. I currently run four Blue Plus and two Blue Specials over my display tank. Not too white, not too blue, good growth.